Within a short time, mobile telecommunications have become a very widespread communications tool which is offering serious competition to established telephone fixed networks and (most importantly) forming a valuable complement to them. As network coverage is being expanded in the industrial countries, the decisive advantage of virtually unrestricted mobility is being exploited to the fullest. Mobile telephones have, therefore, also become a permanent part of the resources for the workers of many companies, organizations and authorities. In addition, companies and institutions within society and social life are increasingly being contacted via means of mobile telephones, even from the outside, as mobile telephones become increasingly widespread.
In this context, the form of the interface between the mobile telephone networks and corporate networks and private branch exchanges is becoming increasingly important. Such an interface should be configured in such a way that subscribers within the corporation or device, that is to say at terminals of the private branch exchange, can be reached as easily and reliably from a mobile telephone network as from a fixed network. In addition, the connection costs should be as low as possible.
However, in this respect, in various countries or telecommunications systems there are still considerable legal, organizational and specific technical restrictions which make access to private networks from mobile telephone networks more difficult.
Thus, in certain countries (for example, South Africa), or owing to restrictions in awarded licenses, it is, under certain circumstances, not possible to implement, in addition to the access into the fixed network in a private branch exchange (PBX), a further access into a mobile telephone network in order to permit calls to be made between the mobile telephone subscribers and subscribers of the private exchange without using the fixed network.
It is known to connect the private branch exchange to a mobile telephone network via a mobile telephone terminal or module which is connected to a private branch exchange. In addition, to increase the capacity of the private branch exchange, a multichannel connection, i.e. connecting a number of mobile telephone modules to one separate call number each, is basically known. However, in this respect there are country-specific legal restrictions; for example, in Germany. In addition, with such an arrangement a caller from the mobile telephone network can discover a free number for dialing into the private branch exchange only by trial and error if he/she dials a busy call number on his/her first dialing attempt. Of course, this constitutes a serious limitation on the usefulness of such a private branch exchange.
The present invention is, therefore, directed toward an improved method of the generic type which makes it possible to dial easily, reliably and cost-effectively into a corporation network from a mobile radio network, and a telecommuncations system with which this method can be executed.
Accordingly, the present invention includes the essential idea of a private branch exchange or comparable device for direct multichannel radio connection to a mobile telephone network being assigned a virtual call number which is common to all the channels. This idea permits common administration of the real call numbers of the mobile telephone channels of the private branch exchange or comparable device, and thus the automatic selection of a free channel for switching through an incoming call to a terminal of the system.
At the private network end, instead of a private branch exchange it is also possible to provide a multiplicity of private branch exchanges or individual lines which can be reached on a virtual call number (what is referred to as a team number). Furthermore, the method is also suitable for voice transmission over an IP network (VoIP=voice-over IP). Instead of a private branch exchange there is then a call server or a VoIP gateway or a comparable entity at the private end.
This idea also can be applied to the connection of a private branch exchange or comparable device to the fixed network. In this case, of course, the private branch exchanges not assigned a number of mobile telephone modules but rather a number of real lines and call numbers under the xe2x80x9cinterfacexe2x80x9d of a common virtual call number. This expanded basic idea of the present invention which includes the connection of a fixed network makes it possible to control the access to corporate networks (call center or the like) from the fixed network, not only (as has been previously known and practiced) as a function of the (geographical) starting point and/or the time of the call, but also as a function of the occupied state of the individual real external lines or call numbers of this network. In this way, better capacity utilization and also cost savings can be achieved in comparison with previously practiced solutions for diverting incoming calls via the public network.
In one preferred embodiment of the proposed solution, a queue of incoming calls is formed in reaction to it being detected that all the real call numbers are busy, and the call is switched through to the desired directly dialed number via the next real call number to become free. In a farther embodiment, the caller can be provided here (in a manner known per se) with a message or interval music or the like to help pass the time while he/she is waiting.
The implementation of the proposed functionality is preferably carried out via an intelligent entity in the public network which is assigned, in particular, to a service administration/service control point there. The implementation will normally essentially take place via software, in which case there are provided, as device aspects, a sensing part for sensing the busy state of the real lines or call numbers and a switching part or control part which is connected to the latter at the input end and have the purpose of selecting a free real call number and switching through the call via said number to the desired internal terminal.
In an additionally advantageous embodiment of the method of the present invention, when there are calls which are outgoing from the private end (from the private branch exchange, from one of the individual lines or from the call server or VoIP gateway), instead of the real number of the calling subscriber another call number is signaled; in particular, the common virtual call number. This can be supplemented in one specific development of this variant with the direct dialing number of the calling subscriber.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.